The multi-antenna technology in the physical layer has become one of the key technologies in the next generation wireless communication system. The multi-antenna technology has a lot of advantages, for instance, the multiplexing gain of the multi-antenna is used for expanding the throughput of the system, the diversity gain of the multi-antenna is utilized for improving the performance of the system, and the directivity gain of the antenna is adopted for distinguishing users to eliminate interference between the users, etc. The LTE (Long Term Evolution) system in the 3GPP (3rd Generation Partnership Project) supports a plurality of MIMO (Multiple-Input Multiple-Output) technologies such as the transmission diversity, spatial multiplexing technology and beam forming, etc.
Currently, both the frame structures of FDD (Frequency Division Duplex) and TDD (Time Division Duplex) in the LTE use the Subframe structure of 1 ms, as shown in FIG. 1, a schematic view of the TDD frame structure, the half-frame of one TDD wireless frame is formed by five Subframes each with 1 ms comprising two Slots of 0.5 ms.
In the system with 5 ms downlink-to-uplink switch-point periodicity, each half-frame includes four Subframes with a length of 1 ms and a special subframe with three Fields: DwPTS, GP and UpPTS. The total length of the three Special Fields is 1 ms. As to the system with 10 ms downlink-to-uplink switch-point periodicity, the first half-frame includes four Subframes with a length of 1 ms and a special subframe with three Fields: DwPTS, GP and UpPTS, and the second half-frame only has five Subframes with a length of 1 ms.
Wherein, the length of the Special Field DwPTS depends upon the configuration type, and the Subframe 0, the Subframe 5 and DwPTS are always reserved for downlink transmission. As shown in FIG. 2, a schematic view of the DwPTS Field, the downlink control signaling is transmitted in the first or first and second OFDM (Orthogonal Frequency Division Multiplexing) symbols in the DwPTS Field, and 72 central subcarriers on the third OFDM symbol are always used to transmit the primary synchronization signal for performing the Cell Search. Expect for the broadcast channel PBCH, any downlink data can occupy the idle resource on this Field for transmission, such as the carrying the physical downlink shared channel PDSCH and the physical multicast channel PMCH, etc.
At present, the LTE system has the following regulations on the downlink beam forming transmission:
The beam forming user uses the UE-specific reference signals to modulate the physical downlink shared channel PDSCH;
The UE-specific reference signals are merely mapped into the resource block for using the beam forming transmission;
The UE-specific reference signals only occupy one antenna port, i.e. the antenna port 5, to perform mapping;
The higher layer needs to inform the UE (User Equipment) whether the UE-specific reference signals are used, i.e. whether the beam forming transmission is performed;
The Cell-specific reference signals on the ports 0, 1, instead of the Cell-specific reference signals on the ports 2, 3 are reserved when the beam forming transmission is performed.
For the LTE TDD system, the Special Field DwPTS can also support the downlink beam forming transmission. However, the current LTE standard merely shows the mapping pattern of the UE-specific reference signals when the beam forming transmission is performed in the normal downlink Subframe, and does not define the mapping pattern of the UE-specific reference signals when the beam forming transmission is performed in the Special Field DwPTS.